Audio transducers provide varying frequency responses based on their physical characteristics, with larger transducers providing a greater response at lower frequencies while smaller transducers provide a more capable response at higher frequencies. With the general frequency range of human hearing spanning three orders of magnitude (approximately 20 Hz to 20 kHz), a single transducer generally cannot faithfully reproduce the full spectrum of audible sound.
Speaker systems that use multiple transducers will often send the low frequency portion of an input signal to a large transducer (or woofer) and the high frequency portion of the input signal to a small transducer (or tweeter). An example of such a system is shown in U.S. Pat. No. 3,947,635, the contents of which are herein incorporated by reference. While dividing an input signal and separately providing it to different sized transducers allows the speaker system to reproduce both high and low sound frequencies, the process introduces audio artifacts that diminish the sound quality. In particular, sound reproduction in the frequency range near the crossover point suffers, as the signal is transitioned from one transducer to another. This is a less than perfect transition, as both transducers share and reproduce the same signal, causing discontinuity, phase shift, frequency peaks and dips occurring within the human voice range (approximately 300-3000 Hz) and across the critical hearing sensitivity range of approximately 1 kHz-5 kHz (Fletcher-Munson/ISO 226-2003 revisions equal-loudness contours). Additionally problematic is the destructive lobbing within this sensitive hearing range due to small frequency wavelengths relative to the distance between the acoustic centers of the woofer and tweeter.
Single column line arrays are loudspeaker systems made up of a number of usually identical transducers mounted in a line and fed an in-phase signal, to create a near-line source of sound. The transducers constructively interfere with each other to send sound waves farther than traditional loudspeakers, and with a more evenly distributed sound output pattern. Vertical columns provide a narrow vertical output pattern that is useful for minimizing reflections (ceiling and floor) and as such attenuates multiple sound arrivals which cause discontinuity and degrade intelligibility.